1. Field of the Invention
The present invention relates to an apparatus for coating a photo-resist film on the surface of a substrate and/or, for developing the photo-resist film subsequent to being exposed with a predetermined pattern, which is used in the manufacture of a semiconductor device, such as an integrated circuit In particular, the apparatus of the invention is effectively used in manufacturing various types of ASICs with small production in each type.
2. Description of the Related Art
In the manufacture of a semiconductor device, such as an integrated circuit (IC), numerous steps for microfabrication are performed to form a device, such as a transistor, in a wafer of, for example, a silicon single crystal. Of these steps, a photoengraving process (PEP) is of greater importance because of PEP provides the base of a present microfabrication technique. In the PEP, a predetermined resist pattern is formed on the surface of the wafer, the resist pattern being employed as, for example, an etching mask.
The formation of the resist pattern by the PEP comprises the steps of coating a photo-resist on the wafer surface to provide a photo-resist film of uniform thickness, selectively exposing the photo-resist film at a predetermined area and developing the exposed photo-resist film to form a desired pattern. In this exposing step, use is made of an exposing device, such as a step and repeat aligner (that is, a stepper). On the other hand, the step for forming the photo-resist film on the substrate surface is carried out with, for example, an apparatus as will be explained below in more detail.
FIG. 1 is a flowchart showing the processing steps of a photo-resist film formation apparatus called a track system, including treating units carrying out a preheating step 4, cooling step 5, coating step 6 and heating step 8. Semiconductor wafers 1 are introduced into the aforementioned apparatus such that each is held within a cassette-like container 2. The semiconductor wafers 1 are taken out of the cassette 2 sheet by sheet and conveyed by a belt conveying mechanism 3 sequentially to the respective units for performing the respective treatment to be carried out there. At the preheating step 4, the wafer 1 has its moisture removed by heating and, subsequent to being cooled by the cooling step 5, is conveyed to the coating unit where a photo-resist is evenly coated on the surface of the wafer 1 by means of, for example, a spinner coater. The photo-resist-coated wafer 1 is sent to the heating unit 8 having a conveyor mechanism 7 called a walking beam system. At the heating unit 8, the photo-resist solution on the wafer is converted into a stable film. At the completion of the heating step 8, a wafer 9 with a desired photo-resist thin film formed thereon is conveyed into cassette 10 where it is stored as a "treated" wafer.
As set out above, in the conventional apparatus, the respective independent treating units are installed in a serial array and a semiconductor wafer to be treated has to be conveyed inevitably past all these units in a "one-way" course in a predetermined order whether all these treatment is required or not. It is, therefore, not possible to freely change a "once-set" treating order or to cause the wafer to pass selectively through only a predetermined unit or units.
The treating process necessary for forming an IC in the semiconductor wafer 1, including its treating sequence, differs depending upon the kinds of IC's to be formed on the wafer. In spite of some step or steps being unnecessary, it is unavoidable in the conventional apparatus that all the aforementioned steps have to be carried out on the semiconductor wafer. This cause a bar to the implementation of improved throughput.
Under this situation, there has been a growing demand for an apparatus which can freely select any particular treating unit or units and can freely change the order for passing through the units in accordance with the kinds of wafers to be treated.